Conventional wireless transmit/receive units (WTRUs) typically comprise a single omni-directional antenna that transmits and receives equally in all directions. Utilizing such antennas, however, significantly wastes WTRU resources as most of a WTRU's energy is used to transmit and receive in directions other than that which is intended. More significantly, this wasted energy is experienced as noise-like interference by nearby WTRUs. Such interference is especially momentous in cases where the uplink (UL) frequency of one WTRU is either the same or near the downlink (DL) frequency of another WTRU. This concept is illustrated in FIG. 1.
FIG. 1 shows a WTRU 102 transmitting omni-directionally. WTRU 104 has an omni-directional receiving beam 112. As the two WTRUs are physically and spectrally close, WTRU 104 experiences significant levels of interference and performance degradation. The interference radius 110 of the interfering WTRU 102 is determined by its own transmission level, the sensitivity of the receiving WTRU 104, the antenna pattern of WTRU 104, and the level of WTRU 104's desired signal. The performance degradation experienced by WTRU 104 reduces the signal-to-interference ratio (SIR) and therefore the signal-to-interference-plus-noise ratio of signals it receives. If significant enough, the interference 120 caused by WTRU 102 can lead to reduced data rates, loss of connection, and/or poor signal quality. This phenomenon is known as WTRU to WTRU (mobile station (MS)-MS) interference.
As described above, WTRUs that utilize omni-directional antennas lack the technology to preferentially control antenna gain so as to minimize the transmitting of unwanted signals toward nearby WTRUs. Similarly, utilizing such antennas prevent WTRUs from rejecting interfering signals emitted from unwanted sources including other nearby WTRUs. Typically, only base stations have been equipped with components and technology to maximize antenna gain in a desired direction while simultaneously limiting the reception of signals in the directions of interfering devices.
Accordingly, it is desirable to have a WTRU than can maximize antenna gain in a desired direction and/or selectively receive signals from a desired direction so as to minimize MS-MS interference.